<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>响应式 - 设备</title>
    <style>
        #outer{
            width: 200px;
            height: 200px;
            background-color: red;
        }

        @media screen and (max-width: 768px) {
            #outer {
                width: 200px;
                height: 200px;
                /* background-color: lightgreen; */
                /* display: none; */
            }
        }
    </style>
</head>
<body>
    <div id="outer">

    </div>
</body>
</html>